Method and apparatus for firing arcuate ceramic segment

ABSTRACT

A setter and method for supporting arcuately formed ceramic, and particularly ferrite, segments during kiln firing. In the preferred embodiment of the setter the segments are supported by opposed, laterally-spaced supporting shelf-like members disposed in angular planes converging downwardly towards the horizontal. The shelf-like members provide line-contact with the outer convex surface of the segment supported thereon.

United States Patent [1' 1 Walker et al.

[ Oct. 30, 1973 METHOD AND APPARATUS FOR FIRING ARCUATE CERAMIC SEGMENT lnventors: Paul J. Walker, Brookfield; Frank C. Barron, Menomonee Falls; Philip F. Walker, Wauwatosa, all of Wis.

Allen Bradley Company, Milwaukee, Wis.

Filed: June 2, 1972 Appl. No.: 259,063

Assignee:

US. Cl. 432/6, 432/259 Int. Cl. F27b 21/04 Field of Search 432/5, 6, 258, 259; 34/239 References Cited UNITED STATES PATENTS 2/1968 Cummings 432/259 3,181,223 5/1965 Cummings 432/259 Primary Examiner.lohn J. Camby Att0meyArnold J. Ericsen et al.

[57] ABSTRACT A setter and method for supporting arcuately formed ceramic, and particularly ferrite, segments during kiln firing. In the preferred embodiment of the setter the segments are supported by opposed, laterally-spaced supporting shelf-like members disposed in angular planes converging downwardly towards the horizontal. The shelf-like members provide line-contact with the outer convex surface of the segment supported thereon.

7 Claims, 3 Drawing Figures FT'TTW 7/7 2/ 2/ MpMsZ/M ig s ssk M A 1 l MZMU METHOD AND APPARATUS FOR FIRING ARCUATE CERAMIC SEGMENT BACKGROUND OF THE INVENTION This invention relates to an improved method and apparatus for supporting and firing an arcuately formed ceramic article, and has particular, immediate application in the field of firing ferrite permanent magnet segments, which are formed for mounting in cylindrical housings for electrical motors to provide the necessary magnetic field excitation. These segments have provided considerable problem in firing, because of their inherent shrinkage characteristics.

In the past, it has been common practice to mount the green, unfired segments with its inner concave surface supported by a refractory form having a convex supporting surface of a dimension which approximates the desired contour of the fired piece. There are at least three major disadvantages involved in the use of the convex forms. First, the forms, being of a relatively dense mass of refractory material must be heated, along with the piece to be fired. Not only does this add cost, but it will be apparent that there is provided an uneven distribution of heat to the respective inner and outer surfaces of the segment during firing. Second, the operator loading the kiln car must be careful in placing the green segment on the form, so as to be sure that it is properly oriented, or it will tend to skew -:during firing. Obviously, such departure from the desired configuration requires additional mechanical grinding operations on those pieces that can even be salvaged. Third, it will be apparent that use of such forms requires vertical spacers for supporting elevated platforms to permit a tiered construction of several parts to utilize as much of the available kiln space as possible. This is at least a cumbersome process. It will be further apparent that heating cost, grinding costs and additional labor costs all add to the aforementioned disadvantages.

Another method of firing arcuate segments, is to merely stand the segments on their ends. This also prevents a serious problem because the ferrite material, in particular, shrinks during firing and the open ends, or free edges, tend to move towards one another. Since the segments are supported on a platform of relatively rough refractory material, the edges tend to drag while the piece shrinks during firing, and will not form the desired arcuate dimension. This again calls for additional grinding operations on salvageable pieces.

It is, accordingly, proposed herein to provide as novel apparatus for accomplishing the novel method what is known in the ceramic tile industry as a setter box, or setter, for supporting the segments during firing. The invention further contemplates the provision of other kiln furniture than that of the preferred mode to accomplish desired results.

Although setters have been known for many years for use as kiln furniture in the flat ceramic tile industry, there does not appear to have been any application for use in supporting arcuate segments during firing, and in particular, supportof arcuate segments made of ferrite material. As a matter of fflCL'IhG present invention in no way contemplates the use of setter boxes in the fashion suggested in their historical usage. For instance, see' U.S. Pat. No. 1,841,641 granted to A. L. Schreiber. This patent illustrates a tile setter, which is used to support relatively flat tiles (FIGS. 2 and 7) and, in addition, discloses in FIG. 1 a supporting plate 13 for arcuate segments 14 supported at their edges in a manner similar to that described above. Other early furniture is disclosed in the U.S. Pat. No. 1,778,561 granted to W. McCoy, U.S. Pat. No. 1,860,374 granted to L. A. Vincent and U.S. Pat. No. 1,848,200 granted to D. V. Robison. A later version is shown as a three-part assembly in the U.S. Pat. No. 2,567,609 granted to J.W.A. Lovatt.

As will be described, the present invention contemplates, in its preferred mode, the use of a setter box approximating the configuration of that disclosed in the U.S. Pat. No. Re. 26,345 granted to H. B. Cummings. The Cummings patent describes a setter box including a plurality of cantilever shelves that are each inclined upwardly with respect to supporting side walls. The opposed, spaced apart shelves are designed to support flat glazed tiles. The patentee states that there is a tendency for the glaze to run and drip down upon the tiles positioned in the lower tiers. By inclining the shelves upwardly, there is provided a gutter" for collecting the glaze. Another reason for providing the patent construction lies in the fact that the upwardly projecting shelves permit support for the flat tiles approximately midway between the center and respective edge of each tile.

The present invention adopts a construction similar to Cummings, but inverts the furniture for entirely different reasons than those proposed by Cummings. The Cummings construction, as illustrated, would not be suitable for use in connection with the present invention.

SUMMARY OF THE INVENTION In accordance with the present invention, there has been provided a novel method and apparatus for kiln firing of arcuately formed segments, and particularly those formed from ferrite material. It is known that this material has a relatively high shrinkage factor during firing, which tends to draw the outer ends of the segment towards one another as the material passes through the firing zone of the kiln. As aforementioned, there have been various methods and kiln furniture employed for supporting the piece as it is traveling through the furnace. There are certain disadvantages, previously outlined, concerning the prior art methods and apparatus.

It is contemplated in the preferred embodiment of the present invention to provide a box-like setter, open at opposed sides, with cantilever shelves projecting from the vertical supporting sides, and preferably formed as an integral unit from refractory material. The cantilevered shelves are preferably inclined downwardly in converging angular planes from opposite sides to permit the green, unfired arcuate segment to be positioned at the outer ends of the laterally spaced shelves. The segment ,is positioned so that the convex outer surface is supported in line-contact with the edges of the opposed shelves. Thus, the segments are free to align themselves with respect to their supporting shelves in accordance with the mass of the members.

' Accordingly, should an operator place the segments on the shelves in offcentefl' fashion, the piece or member will settle into position as the setter box is jostled along its path through the furnace. The line-contact between the arcuate segment and its respectivesupporting shelves provides the least resistance for accomplishing the correct alignment.

Excellent results have been obtained in accordance with the method as used in conjunction with the setter of the present invention, and in particular, the setter box as described above. However, it will be apparent that the method of the present invention may be practiced with other support means capable of providing line-contact with the opposite sides of the upright arcuate segment. The particular setter of the preferred embodiment provides additional advantages, in that the downwardly inclined shelves are readily adaptable for receiving segments of varying sizes. That is, an individual setter box may include segments of varying sizes, or the same setter box may be used without change of dimension for segments of the same size, but differing from those in like setters as they move'through the kiln.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view of a box-like setter made according to this invention.

FIG. 2 is top view, partly in section, taken along lines 2-2 of FIG. 1.

FIG. 3 is a perspective view of a single arcuately formed segment as fired in accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT A method of firing arcuate ceramic segments in accordance with the present invention will be described in conjunction with the novel preferred embodiment of apparatus in form of a refractory box-like setter illustrated in FIGS. 1 and 2.

The box-like setter comprises an open sided construction having a pair of side walls 11, and may have intermediate support walls 12 to define a plurality of cells should size of the supported pieces permit. That is, it will be obvious that economy of space will determine the number of cells to be defined. The side walls 11 and intermediate supporting walls 12 terminate in a bottom 13 and a top 14. The bottom 13 rests upon either a conveyor platform, a kiln car or, of so desired, directly upon the top of another setter box positioned therebelow (not shown). That is, in interest of economy, a number of setter boxes 10 may be stacked one above the other, if so desired. The support for the low ermost setter box 10 is denoted by the reference numeral l6.

The setter box 10 is designed so as to permit an open front and back defined by the side walls 11, the intermediate supporting walls 12, the bottom 13 and the top 14.

A plurality of cavities are defined by the upright side walls 11 and intermediate support walls 12 and their respective opposed, parallel shelves 18 formed integrally therewith. The shelves 18 are substantially coextensive with the width of the respective support walls 11 and 12 (see FIG. 2) and are inclined downwardly from the horizontal at a desired angle a for purposes hereinafter described. Each pair of shelves 18 are also parallel with the bottom 13. It is also preferable to form the shelves 18 with a downwardly inclined undersurface 21 to afford additional space in the cavity or cell for larger size segments, as will hereinafter be described.

It will be apparent that the ultimate size of the cavities defined by the walls 11 and 12 and opposed shelves 18 may be selected to accommodate several sizes of arcuate segments 25a, 25b, 25c and 25d, as shown in FIG. 1. The length and angle of the shelves 18 is determined by several factors. That is, the downward inclination of the surface 20 provides an approximate line-contact between the segments 25a, 25b, 25c and 25d and their respective supporting upper surfaces 20 of the shelves 18 as indicated by the facing arrows in the view of FIG. 1. Other factors include space requirements and spacing between the opposite edges of the shelves for permitting entrance of loading and unloading devices (not shown).

The top view of FIG. 2 illustrates a typical arrangement of a plurality of segments 25a as they are disposed upon the surfaces 20 of the laterally spaced shelves 18.

It will be apparent from the foregoing that the present invention provides for a new method for firing arcuate segments, wherein the segments 25a, 25b, 25c and 25d are positioned to provide a line-contact between the segments and their respective support member or shelves 18. That is, the line-contact is made between the surface 20 of the support shelves 18 and the outer, or convex, surface of the respective segments at points substantially equidistant from the center of the piece. Should the piece of segment be positioned, prior to firing, in a slightly off-center fashion, the segment will naturally tend to settle with its mass locating itself with its center of gravity being in substantial alignment with a vertical plane bisecting the segment. This will provide a symmetrical support at the points of line-contact as the setter box 10 or other support means is traveling through the entering zone of the kiln. Natural movement of the kiln car or conveyor will provide the necessary vibrations to permit the segments to settle into the desired position for firing. The vertical alignment will insure that the free ends of the segments will shrink symmetrically towards one another.

The various disadvantages of firing of the segments while standing on their ends and over convex forms will be avoided. It will be obvious that the open ended setter box 10, or other means of providing line-contact with the segment, will permit free flow of the heated air or other firing atmosphere substantially uniformly about the entire surface of the segment. The dense mass of refractory supports in the past have prevented this uniform heating, and the supports themselves have taken up both space and extra heat. The open edges of the segment are free to move inwardly towards one another as the piece shrinks during firing. As stated above, when the pieces have been edge fired, while being placed in an up ended position on a flat surface, one or both of the edges very often tend to drag and provide an unsymmetrical piece.

Great savings in grinding costs are obtained by the present method, since the segment is free to attain its desired symmetry during firing. There was a certain amount of waste in the past of pieces that could not even be ground to final shape, and this has been materially reduced by the method of the present invention.

Obviously, other means for providing line-contact between the segment and the support fall within the province of this invention, but do not offer the advantages of the above described box-like setter 10. For instance, it will be apparent that the piece might be positioned between spaced apart cylinders, but the additional mass of these refractory pieces do not permit ease in loading and unloading and also provides certain disadvantages in free flow of the firing atmosphere.

I claim:

1. The method of firing green arcuate ceramic segments comprising the steps of providing a refractory supporting setter having paired, laterally spaced supporting surfaces for supporting the outer convex surface of the respective segments in line-contact supporting relationship at either side of a plane bisecting said segments, placing a green arcuate segment on a respective pair of laterally spaced supporting surfaces with its free edges facing upwardly, and firing said supported segment and said supporting setter.

2. The method of claim 1 including, in the step of providing a setter as defined therein, providing a setter having opposed vertical walls, each of said walls carrying an internal shelf extending toward an internal shelf carried by the opposite vertical wall, and wherein the oppositely disposed shelves have relatively flat upper surfaces lying in a downwardly converging planes relative to the horizontal.

3. The method of claim 2 including, in the step of providing the setter as defined therein, providing a setter with said oppositely disposed shelves being vertically spaced to accommodate arcuate segments of varying size.

4. A setter for firing arcuately formed ceramic segments comprised of opposed vertical support walls; a

plurality of vertically spaced cantilever shelves carried by each of said support walls, said shelves carried by said walls being arranged in oppositely disposed pairs, the upper surface and the under surface of each of said oppositely disposed shelves being inclined to lie in downwardly converging planes, whereby, when an arcuately formed segment is supported on the respective upper surfaces of said oppositely disposed shelves it will contact said surfaces in substantial line-contact therewith at either side of a plane bisecting said arcuate segment, and whereby the free ends of a segment disposed on a pair of shelves will be free of interference with inclined under surfaces of the pair of shelves disposed immediately thereabove.

5. A setter as defined in claim 4, including a top and a bottom joining each of said vertical support walls to define an open-sided, box-like construction.

6. A setter as defined in claim 4, wherein each of said shelves is integrally formed with its respective vertical support wall and laterally spaced from the shelf oppositely disposed therefrom.

7. A setter as defined in claim 5, wherein said boxlike construction includes a plurality of said vertical support walls, eachsupporting a plurality of vertically spaced, opposed pairs of said shelves.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 1 3,768,963 mm! October 30, 1973 Paul J. Walker, Frank C. Barron) Philip F. Walker Inventor) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, Lines 40 & 41 "prevents" should read pre sents-- Column 5, Line 18 Delete -aafter "in" and before "downwardly" Signed and sealed this 16th day of April 197M (SEAL) Attest:

EDWARD I-.I.I LETCHEI-I,JR. C. MARSHALL DANN Attosting Officer- Commissioner of Patent 

1. The method of firing green arcuate ceramic segments comprising the steps of providing a refractory supporting setter having paired, laterally spaced supporting surfaces for supporting the outer convex surface of the respective segments in line-contact supporting relationship at either side of a plane bisecting said segments, placing a green arcuate segment on a respective pair of laterally spaced supporting surfaces with its free edges facing upwardly, and firing said supported segment and said supporting setter.
 2. The method of claim 1 including, in the step of providing a setter as defined therein, providing a setter having opposed vertical walls, each of said walls carrying an internal shelf extending toward an internal shelf carried by the opposite vertical wall, and wherein the oppositely disposed shelves have relatively flat upper surfaces lying in a downwardly converging planes relative to the horizontal.
 3. The method of claim 2 including, in the step of providing the setter as defined therein, providing a setter with said oppositely disposed shelves being vertically spaced to accommodate arcuate segments of varying size.
 4. A setter for firing arcuately formed ceramic segments comprised of opposed Vertical support walls; a plurality of vertically spaced cantilever shelves carried by each of said support walls, said shelves carried by said walls being arranged in oppositely disposed pairs, the upper surface and the under surface of each of said oppositely disposed shelves being inclined to lie in downwardly converging planes, whereby, when an arcuately formed segment is supported on the respective upper surfaces of said oppositely disposed shelves it will contact said surfaces in substantial line-contact therewith at either side of a plane bisecting said arcuate segment, and whereby the free ends of a segment disposed on a pair of shelves will be free of interference with inclined under surfaces of the pair of shelves disposed immediately thereabove.
 5. A setter as defined in claim 4, including a top and a bottom joining each of said vertical support walls to define an open-sided, box-like construction.
 6. A setter as defined in claim 4, wherein each of said shelves is integrally formed with its respective vertical support wall and laterally spaced from the shelf oppositely disposed therefrom.
 7. A setter as defined in claim 5, wherein said box-like construction includes a plurality of said vertical support walls, each supporting a plurality of vertically spaced, opposed pairs of said shelves. 